Macrophages release mediators which affect the metabolic activities of certain ocular cells. Human blood monocytes secrete in vitro a factor which enhances the DNA synthesis of human corneal cell cultures. On chromatography, the factor was located within the molecular range of 40,000-50,000 daltons. It is possible this mediator plays a role in wound healing. The effects of a lipid storage compound, glucocerebroside (GL1), were tested on macrophage cultures. This compound, which accumulates in cells of Gaucher's disease patients, stimulates the secretion of a mediator, lymphocyte activating factor (LAF) from both human and mouse macrophages. Moreover, GL1 in synergy with another stimulant, endotoxin, causes the secretion of extremely high levels of LAF by macrophages. In addition, GL1 increases the release of lysosomal enzymes by the mouse macrophage cultures. Both LAF and the enzymes may possibly be related to certain features of the Gaucher's disease.